Methods for taking an image of the inside of an examined subject (hereinafter, “patient”) by using an X-ray Computed Tomography (CT) apparatus are conventionally known. Examples of the known methods include a method for taking an image of the inside of a patient who is in a breath-holding state, an exhalation-period state, and an inhalation-period state. The examples of the known methods also include a method for taking an image of the inside of a patient in correspondence with a plurality of temporal phases, without specifying any respiratory state of the patient. Further, in recent years, X-ray CT apparatuses capable of imaging the inside of a patient over a large area and in a three-dimensional manner are also known. Thus, in some situations, an image of the inside of a patient is taken by using such X-ray CT apparatuses. These X-ray CT apparatuses are used for, for example, taking an image of a tumor inside a patient.